• Energy Research
• computer and information sciences close

Most of wireless sensors are dynamically changing and execute two types of tasks: hard deadline periodic ones and aperiodic ones with no deadline. The emergence of energy harvesting technologies makes it possible to design self-powered sensors through environmental energy. Nevertheless, classical scheduling techniques need to be reconceived so as to take into account the fluctuating energy source and energy consumptions of tasks. Hence, we firstly describe the called TB-H and TB*-H aperiodic task servers which are extensions of the famous Total Bandwidth server. We show how TB-H and TB*-H permit to provide short response times for the aperiodic tasks by computing adequate virtual deadlines taking into account both time and energy constraints. Our second contribution lies in extensive simulations to bring to light the effectiveness of these two novel Bandwidth based servers in comparison to basic background approaches.

The parametric design method of equal and unequal thickness reverse thrust blades is studied based on the cubic Bessel curve controlled by four control points. In order to improve the aerodynamic performance of the thrust reverser and reduce the structure weight, the geometry shape of the blade in the three-dimensional thrust reverser cascade assembly was optimized by using a genetic algorithm based on BP artificial neural network, and the fluid-structure coupling and modal analysis of the optimized thrust reverser cascade were carried out. The results show that: compared with the benchmark model, the thrust reverses of the optimized equal thickness and non-equal thickness blades are increased by 15.64 and 12.71%, respectively, and the flow rate increases by 11.32 and 13.52%, respectively; based on the optimized blade profile, increasing the number of stiffeners is more efficient than increasing the thickness of cascade assembly in the area of reducing the maximum stress and strain; Increasing the number of stiffeners and the thickness of cascade assembly can improve the first-order natural vibration frequency of the cascade assembly.

AbstractA quantitative risk assessment method of casing collapse resistance and internal pressure resistance is established in accordance with the theory of structural reliability and random theory, in terms of geometrical parameters, mechanical property and external load randomness of casing and on the basis of the analysis on shortcomings of safety coefficient and assessment methods for conventional casing design. Using Monte-Carlo random sampling method, a probability of casing failure with different pressure and a relationship between safety coefficient and probability of casing failure have been obtained by simulating a random distribution regularity of casing strength. Studies show that quantitative risk assessment methods could be adopted to perform quantitative assessment on casing safety and reliability. Casings of different types and under the effect of different external loads have similar safety coefficient and different probabilities of failure. Failure probability assessment index calculated with random theory may provide bases for the selection of conventional safety coefficient and casing design and assessment with uncertain external loads.

Rock drillability is a comprehensive index that indicates the ease of drilling a hole in the rock mass, which is a main basis for the design of drilling bits, the optimization of drilling operational parameters, and the prediction of rate of penetration. This paper established a conversion relationship between mechanical specific energy measured from micro-drilling tests and mechanical specific energy measured from scratch tests, based on the consistency of rock breaking mechanism between these two types of tests. By incorporating the methodology of calculating rock drillability grade of polycrystalline diamond compact bits, a new mathematical model for predicting rock drillability of polycrystalline diamond compact bits is developed. Subsequently, a new method for acquiring continuous rock drillability profile by scratching the core surface is developed. A wide range of rocks with different hardness were tested by the proposed scratch method. The results show that the new model has high consistency with the results of laboratory micro-drilling tests. For example, the average errors of sandstone, shale, and carbonate test results are only 7.41%, 8.18%, and 4%, respectively. The new method can fully characterize the effect of mineral composition, cementation strength, and microstructure of rock on drillability. Besides, the new model has high utilization efficiency of expensive core samples because the core usually remains nondestructive after scratch tests.

Abstract The leader election problem is one of the fundamental problems in distributed computing. Different from most of the existing results studying the multi-leader election in static networks or one leader election in dynamic networks, in this paper, we focus on the multi-leader election in dynamic sensor networks where nodes are deployed randomly. A centralized simple leader election algorithm (VLE), a distributed leader election algorithm (NMDLE), and a multi-leader election algorithm (PSMLE) are proposed so as to elect multi-leaders for the purpose of saving energy and prolonging the network lifetime, respectively. Specifically, the proposed algorithms aim at using less leaders to control the whole network, which is controlled by at least k opt leaders, here k opt denotes the optimal number of network partitions. Then we analyze the impacts of the sleep scheme of nodes and node moving on energy consumption and establish a theoretical model for energy cost. Finally, we provide extensive simulation results valuating the correctness of theoretical analysis.

Abstract Energy of a molecule plays an important role in physics, chemistry and biology. In mathematics, the concept of energy is used in graph theory to help other subjects such as chemistry and physics. In graph theory, nullity is the number of zeros extracted from the characteristic polynomials obtained from the adjacency matrix, and inertia represents the positive and negative eigenvalues of the adjacency matrix. Energy is the sum of the absolute eigenvalues of its adjacency matrix. In this study, the inertia, nullity and signature of the aforementioned structures have been discussed.

AbstractThe energy of a graph is the sum of the moduli of the eigenvalues of its adjacency matrix. Integral circulant graphs can be characterised by their order n and a set D of positive divisors of n in such a way that they have vertex set Z/nZ and edge set {(a,b):a,b∈Z/nZ,gcd(a-b,n)∈D}. Among integral circulant graphs of fixed prime power order ps, those having minimal energy Eminps or maximal energy Emaxps, respectively, are known. We study the energy of integral circulant graphs of arbitrary order n with so-called multiplicative divisor sets. This leads to good bounds for Eminn and Emaxn as well as conjectures concerning the true value of Eminn.

The energy of a graph is the sum of the absolute values of the eigenvalues of its adjacency matrix. Koolen and Moulton have proved that the energy of a graph on n vertices is at most n(1 + √n)/2, and that equality holds if and only if the graph is strongly regular with parameters (n, (n+√n)/2, (n+2√n)/4, (n+2√n)/4). Such graphs are equivalent to a certain type of Hadamard matrices. Here we survey constructions of these Hadamard matrices and the related strongly regular graphs.